Devices having high dielectric constant, ionically-polarizable materials

ABSTRACT

An electronic or electro-optic device has a first electrode, a second electrode spaced apart from the first electrode, and a dielectric layer disposed between the first and second electrodes. The dielectric layer has electrically insulating planar layers with intercalated ions therebetween such that the electrically insulating planar layers provide a barrier to impede movement of the intercalated ions to the first and second electrodes under an applied voltage while permitting a polarization of the dielectric layer while in operation.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.61/010,289 filed Jan. 7, 2008, the entire contents of which are herebyincorporated by reference.

This invention was made using U.S. Government support under AFOSR GrantNo. FA9550-06-1-0076 and DOE Grant No. 37420-001-06. The U.S. Governmenthas certain rights in this invention.

BACKGROUND

1. Field of Invention

The current invention relates to electronic and/or electro-opticdevices, and more particularly to electronic and/or electro-opticdevices that include high dielectric-constant, ionically-polarizablematerials.

2. Discussion of Related Art

There are numerous approaches to high-capacitance devices includinghigh-dielectric constant (high-∈) insulators, ultrathin dielectricfilms, and/or high surface area electrodes. In silicon electronics, SiO₂gate dielectrics that capacitively couple gate voltages to the formationof semiconductor charge carrier channels were shrunk to just a fewmonolayers before reaching a fundamental breakdown limit; as a result,higher-∈ HfO₂ was introduced as a replacement. (S. Duenas, H. Castan, H.Garcia, A. Gomez, L. Bailon, M. Toledano-Luque, I. Martil, and G.Gonzalez-Diaz, Electrical properties of high-pressure reactive sputteredthin hafnium oxide high-k gate dielectrics, Semiconductor Science andTechnology 22, 1344 (2007); G. He, L. Q. Zhu, M. Liu, Q. Fang, and L. D.Zhang, Optical and electrical properties of plasma-oxidation derivedHfO2 gate dielectric films, Applied Surface Science 253, 3413 (2007); H.Wong and H. Iwai, On the scaling issues and high-kappa replacement ofultrathin gate dielectrics for nanoscale MOS transistors,Microelectronic Engineering 83, 1867 (2006); D. Q. Wu, H. S. Zhao, J. C.Yao, D. Y. Zhang, and A. M. Chang, Development of high-k gate dielectricmaterials, Journal of Inorganic Materials 23, 865 (2008).) For energystorage, double-layer capacitors utilize the self-limiting thickness ofpolarized ionic assemblies in solution along with high surface areaelectrodes made from metallic solids and/or high surface area carbons.(B. B. Garcia, A. M. Feaver, Q. F. Zhang, R. D. Champion, G. Z. Cao, T.T. Fister, K. P. Nagle, and G. T. Seidler, Effect of pore morphology onthe electrochemical properties of electric double layer carbon cryogelsupercapacitors, Journal of Applied Physics 104 (2008); C. W. Huang, C.M. Chuang, J. M. Ting, and H. S. Teng, Significantly enhanced chargeconduction in electric double layer capacitors using carbonnanotube-grafted activated carbon electrodes, Journal of Power Sources183, 406 (2008); K. Juodkazis, J. Juodkazyte, V. Sukiene, A.Griguceviciene, and A. Selskis, On the charge storage mechanism atRuO2/0.5 M H2SO4 interface, Journal of Solid State Electrochemistry 12,1399 (2008); D. Pech, D. Guay, T. Brousse, and D. Belanger, Concept forcharge storage in electrochemical capacitors with functionalized carbonelectrodes, Electrochemical and Solid State Letters 11, A202 (2008); M.M. Shaijumon, F. S. Ou, L. J. Ci, and P. M. Ajayan, Synthesis of hybridnanowire arrays and their application as high power supercapacitorelectrodes, Chemical Communications, 2373 (2008); C. Z. Yuan, H. Dou, B.Gao, L. H. Su, and X. G. Zhang, High-voltage aqueous symmetricelectrochemical capacitor based on Ru0.7Sn0.3O2 center dot nH(2)Oelectrodes in 1 M KOH, Journal of Solid State Electrochemistry 12, 1645(2008).) The combination of double layer formation and redox processesat the electrode surfaces, which can involve the metallic species orconductive polymer adlayers, leads to a synergistic effect known assupercapacitance. (P. K. Nayak and N. Munichandraiah, Cobalt hydroxideas a capacitor material: Tuning its potential window, Journal of theElectrochemical Society 155, A855 (2008); J. Oh, M. E. Kozlov, B. G.Kim, H. K. Kim, R. H. Baughman, and Y. H. Hwang, Preparation andelectrochemical characterization of porous SWNT-PPy nanocomposite sheetsfor supercapacitor applications, Synthetic Metals 158, 638 (2008); R. K.Sharma, A. C. Rastogi, and S. B. Desu, Manganese oxide embeddedpolypyrrole nanocomposites for electrochemical supercapacitor,Electrochimica Acta 53, 7690 (2008); J. F. Zang, S. J. Bao, C. M. Li, H.J. Bian, X. Q. Cui, Q. L. Bao, C. Q. Sun, J. Guo, and K. R. Lian,Well-aligned cone-shaped nanostructure of polypyrrole/RuO2 and itselectrochemical supercapacitor, Journal of Physical Chemistry C 112,14843 (2008); H. B. Zhang, H. L. Li, F. B. Zhang, J. X. Wang, Z. Wang,and S. C. Wang, Polyaniline nanofibers prepared by a facileelectrochemical approach and their supercapacitor performance, Journalof Materials Research 23, 2326 (2008).) In another alternative, flexiblecapacitive sheets with highly nonpolar or ferroelectric polymericdielectrics (Q. Chen, B. J. Chu, X. Zhou, and Q. M. Zhang, Effect ofmetal-polymer interface on the breakdown electric field ofpoly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)terpolymer, Applied Physics Letters 91 (2007); Q. Chen, Y. Wang, X.Zhou, Q. M. Zhang, and S. H. Zhang, High field tunneling as a limitingfactor of maximum energy density in dielectric energy storagecapacitors, Applied Physics Letters 92 (2008); B. J. Chu, X. Zhou, K. L.Ren, B. Neese, M. R. Lin, Q. Wang, F. Bauer, and Q. M. Zhang, Adielectric polymer with high electric energy density and fast dischargespeed, Science 313, 334 (2006); J. Claude, Y. Y. Lu, K. Li, and Q. Wang,Electrical storage in poly(vinylidene fluoride) based ferroelectricpolymers: Correlating polymer structure to electrical breakdownstrength, Chemistry of Materials 20, 2078 (2008); M. Rabuffi and G.Picci, Status quo and future prospects for metallized polypropyleneenergy storage capacitors, IEEE Transactions on Plasma Science 30, 1939(2002); Z. C. Zhang and T. C. M. Chung, The structure-propertyrelationship of poly(vinylidene difluoride)-based polymers with energystorage and loss under applied electric fields, Macromolecules 40, 9391(2007)) flanked by metal coatings are coiled to increase capacitance perunit volume. Consequently, there remains a need for electronic and/orelectro-optic devices that have improved dielectric structures.

SUMMARY

An electronic or electro-optic device according to an embodiment of thecurrent invention has a first electrode, a second electrode spaced apartfrom the first electrode, and a dielectric layer disposed between thefirst and second electrodes. The dielectric layer has electricallyinsulating planar layers with intercalated ions therebetween such thatthe electrically insulating planar layers provide a barrier to impedemovement of the intercalated ions to the first and second electrodesunder an applied voltage while permitting a polarization of thedielectric layer while in operation.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features of this invention are provided in the followingdetailed description of various embodiments of the invention withreference to the drawings. Furthermore, the above-discussed and otherattendant advantages of the present invention will become betterunderstood by reference to the detailed description when taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a schematic illustration of the crystal structure of sodiumbeta-Alumina.

FIG. 2 is a schematic illustration to describe several electronic and/orelectro-optic devices according to some embodiments of the currentinvention. It shows a general sample layout that can also be used fortesting layered oxide dielectric-semiconductor oxide bilayers.Individual top electrodes can complete capacitors. Pairs of topelectrodes can act as source-drain contacts for FETs. Penetration of thesemiconductor part way into the dielectric is possible.

FIG. 3 shows the capacitance (left) and conductance (right) at 1 MHz foran Al/ZnO/Ta₂O₅/Si capacitor showing tenfold capacitance increase inaccumulation. (from Nandi et al.)

FIG. 4 shows an XRD pattern of the gel-derived SBA powder afterannealing at 840° C.

FIG. 5 shows the frequency dependent capacitance (C vs f) of the 75 nmITO/SAB/Au structure.

FIG. 6 shows the cross-sectional SEM of SBA (upper lighter coloredlayer) on a silicon wafer.

FIG. 7 shows the output characteristics of a ZnO FET with SBAdielectric, with W/L=50.

FIG. 8 shows the output characteristic for a ZTO transistor fabricatedon ITO quartz substrate with W/L=10.

FIG. 9 shows the capacitance-voltage plot for ITO-SBA-Au at fourfrequencies.

FIG. 10 shows the Capacitance-voltage plot for ITO/SBS/ZTO/Al taken on atransistor with threshold voltage of 0.6 V. The capacitance was measuredat 250 Hz.

FIG. 11-13 illustrate open atmosphere I_(D)-V_(D)) characteristics ofZnO transistors with a drain voltage of 1V, 2V, and 3V, respectively.

FIG. 14 shows I_(D)-V_(D) characteristics with higher gate voltage(V_(G)) and drain voltage (V_(D)).

FIG. 15 shows I_(D)-V_(G) measurements (transfer characteristics) of theZnO FET with a 20 volt source-to-drain voltage in an ambient atmosphere.

FIG. 16 shows the same transfer characteristics as in FIG. 15, but on asemi-log scale.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

Some embodiments of the current invention are discussed in detail below.In describing embodiments, specific terminology is employed for the sakeof clarity. However, the invention is not intended to be limited to thespecific terminology so selected. A person skilled in the relevant artwill recognize that other equivalent components can be employed andother methods developed without departing from the broad concepts of thecurrent invention. All references cited herein are incorporated byreference as if each had been individually incorporated.

There are extensive research programs aimed at the development and useof ionic conductors for batteries and fuel cells in which the migrationof ions through a solid contributes to direct current in a powercircuit. (S. Q. Hui, J. Roller, S. Yick, X. Zhang, C. Deces-Petit, Y. S.Xie, R. Marie, and D. Ghosh, A brief review of the ionic conductivityenhancement for selected oxide electrolytes, Journal of Power Sources172, 493 (2007); V. Thangadurai and W. Weppner, Recent progress in solidoxide and lithium ion conducting electrolytes research, Ionics 12, 81(2006); E. V. Tsipis and V. V. Kharton, Electrode materials and reactionmechanisms in solid oxide fuel cells: a brief review, Journal of SolidState Electrochemistry 12, 1039 (2008).) However, devices conventionallyutilize these materials as electrolytes and do not recognize thatmaterials that have intercalated ions between electrically insulatingplanes can exhibit desirable dielectric propoerties for use asdielectric structures in electronic and/or electro-optic devices. Theconventional conductor circuits rely on ions entering and exiting thesolid, exchanging with other circuit elements. However, in cases wherethe ions cannot migrate into and out of a solid at as fast a rate or inas large a quantity as electrons or holes in an external circuit, theybecome positionally polarized within the solid by electric fields andthus contribute to capacitance, not DC conductivity. The mechanism ofionic motion within an ionic conductor can therefore lead to eithercapacitance or conductivity depending on the ability of electrodes toaccept and inject the ions, and the time scale of the observation.Therefore, according to some embodiments of the current invention, ionicconductors are used as ionically polarizable dielectric insulators withenhanced energy storage ability.

An embodiment of a dielectric material 100, for use in electronic and/orclectro-optic devices according to some embodiments of the currentinvention is illustrated schematically in FIG. 1. The dielectricmaterial 100 has a plurality of electrically insulating planes, such aselectrically insulating planes 102, 104 and 106, with pluralities ofintercalated ions 108, 110 therebetween. For example, one ion of theplurality of intercalated ions 108 between electrically insulatingplanes 102 and 104 is indicated at reference numeral 112. In FIG. 1,only a small section of the dielectric material 100 is illustrated.Sodium beta-alumina (SBA) is one example of a dielectric material 100that can be used as a high-dielectric-constant, ionically-polarizablefilm material according to some embodiments of the current invention.SBA is one example of a layered crystal that that exhibits very highionic conductivity in two dimensions. (See, for example, Y. Lecars, J.Thery, and Collongu. R, Nonstoichiometry and Stability of Beta′ andBeta″ Alumina, Comptes Rendus Hebdomadaires Des Seances De L AcademieDes Sciences Serie C 274, 4 (1972); H. Nafe, F. Meyer, and F. Aldinger,The equilibrium between Na-beta- and Na-beta″-alumina as a function ofthe phase composition, Electrochimica Acta 45, 1631 (2000); K. Shqau andH. Nafe, Thermodynamic stability of potassium-beta-alumina, Journal ofthe American Ceramic Society 88, 2894 (2005); F. Vandecruys, E. Brauns,J. Vangrunderbeek, and R. V. Kumar, Thermodynamic activity of Na2O in Nabeta-alumina, Materials Research Bulletin 35, 1153 (2000); Whitting. Msand R. A. Huggins, Measurement of Sodium Ion Transport in Beta Aluminausing Reversible Solid Electrodes, Journal of Chemical Physics 54, 414(1971); Whitting. Ms and R. A. Huggins, Inherent Transport Properties ofBeta-alumina Family, Journal of the Electrochemical Society 119, C109(1972) for some background information regarding some of thesematerials.) The conductivity can be observed in powder form (S. Sartori,A. Martucci, A. Muffato, and M. Guglielmi, (2004), p. 911. Contact FreeConductivity of Layered Materials—Na Beta-alumina, Journal of AppliedPhysics 50, 5761 (1979)) as well as in films, and is of major importancefor use as a solid-state electrolyte (U. Strom, P. C. Taylor, and S. G.Bishop, Electrical-conductivity Spectrum of Na Beta Alumina from 109 to1013 HZ, Bulletin of the American Physical Society 20, 330 (1975)),particularly for high-temperature battery applications. (J. L. Sudworth,P. Barrow, W. Dong, B. Dunn, G. C. Farrington, and J. O. Thomas, Towardcommercialization of the beta-alumina family of ionic conductors, MrsBulletin 25, 22 (2000).) Although reference is made to sodium betaalumina as an example throughout this specification, other structuressuch as sodium beta″ alumina (beta double prime alumina) can also beused in other embodiments of the current invention. Furthermore, thegeneral concepts of the current invention are not limited to only theseparticular examples. Other materials that have electrically insulatingplanes (in a direction perpendicular to the planes) with intercalatedions therebetween may be used in other embodiments of the currentinvention.

The ionic conductivity of SBA is due to the motion of sodium ions in thelattice planes, which are separated by a distance of 11.3 Å. At leasttwo regimes of ionic displacement have been identified in layeredaluminas (K. Funke and R. D. Banhatti, (2007), p. 1942.), and the ionicconductivity is substantial even through the gigahertz regime. Betweenthe planes are non-conducting spinel-type blocks of Al and O ions,greatly lowering the ionic conductivity in the direction perpendicularto the planes. Furthermore, instead of being high ionic conductor, it'selectron conductivity is very poor which implies SBA's dc resistivity isextremely high like alumina. For this reason, a thin layer of SBA may beused as a gate insulator, for example, of a field effect transistor(FET) in an embodiment of the current invention so that it cancontribute very small gate leakage current in the transistorcharacteristics. Additionally, applying a very small gate voltage chargeseparation between the two surfaces of the gate insulator film may bepossible. Using this ion conducting insulator, a low operating voltageVET can be fabricated according to an embodiment of the currentinvention. These properties arise out of the SBA layered structure,which ensures a very large anisotropy in the ionic conductivity, unlikemore three-dimensional ionic conductors or oxides with a degree ofelectronic conductivity as well. However, the broad concepts of thecurrent invention are not limited to only SBA. Other embodiments of thecurrent invention include other materials that have insulating planesthat prevent intercalated ions from moving through the planes whilepermitting ionic polarizability of the material due to shift of the ionswithin the interplane regions.

SBA crystal can be synthesized in an embodiment of the current inventionby a simple solution approach, i.e by a sol-gel route. First, we preparea clear gel from which SBA crystal can be prepared according to anembodiment of the current invention. Then this solution can be spincoated over a highly dope Si wafer in one example. After this, the gelderived glass can be annealed at a high temperature to obtaincrystalline SAB. In this example, a sufficient time heat treatment wasgiven to obtain a maximum amount of crystal phase.

FIG. 2 is a schematic illustration of an electronic or electro-opticdevice 200 according to an embodiment of the current invention. Theelectronic or electro-optic device 200 has a first electrode 202, asecond electrode 104 spaced apart from the first electrode 202, and adielectric layer 206 disposed between the first and second electrodes.The dielectric layer 206 has electrically insulating planar layers withintercalated ions therebetween, such as, but not limited to, dielectricmaterial 100. The electrically insulating planar layers provide abarrier to impede movement of the intercalated ions to prevent them frommoving to the first and second electrodes 202, 204 under an appliedvoltage while permitting a polarization of the dielectric layer 206while the electronic or electro-optic device 200 is being operated. Theinvention is not limited to the materials selected for the electrodes.The materials for the electrodes can be selected from conventionallyavailable or newly developed materials for electrodes. For example, theycan be, but are limited to, transparent electrodes for someapplications. Furthermore, the electrodes can be formed on substrates insome embodiments of the current invention. The substrates can be, butare not limited to, transparent substrates in some embodiments of thecurrent invention. For example, glass and/or plastic substrates can beused in some embodiments of the current invention.

In FIG. 2, the electronic or electro-optic device 200 is alsoillustrated as having a semiconductor layer 208 between the dielectriclayer 206 and the first electrode 202. In some embodiments, thesemiconductor layer 208 is not present. For example, the electronic orelectro-optic device 200 can be a capacitor having only the first andsecond electrodes 202, 204 such that the first and second electrodes202, 204 are in contact with the dielectric layer 206. In otherembodiments the semiconductor layer can be a hybridsemiconductor-dielectric material in which molecules of the hybridmaterial have a semiconducting portion and a dielectric portion. Thedielectric layer 206 is not limited to any specific number of insulatingplanes. For example there can be two, three, or more than threeinsulating planes with intercalated ions therebetween in the dielectriclayer 206 according to some embodiments of the current invention.Furthermore, there can be dielectric layers in addition to thedielectric layer 206, such as dielectric layers of conventionally usedmaterials in addition to dielectric layer 206. One particular example,without limitation, could be a case in which the second electrode isformed on a silicon substrate in which the silicon substrate has a thinSiO₂ layer. Furthermore, electronic or electro-optic devices 200according to some embodiments of the current invention can have multipledielectric and/or multiple semiconductor layers as well as additionallayers of material between the first and second electrodes withoutdeparting from the general scope of the current invention.

The electronic or electro-optic device 200 can also have a thirdelectrode 210 in some embodiments of the current invention. For example,the electronic or electro-optic device 200 can be a field effecttransistor (FET) in some embodiments of the current invention such thatthe second electrode 104 is a gate electrode and the first and thirdelectrodes 202, 210 are source and drain (or vice versa) electrodes. Theelectronic or electro-optic device 200 is not limited to two or threeelectrodes and can have additional electrodes such as electrodes 212 and214, for example, or even more if desired for the particularapplication.

The semiconductor layer 208 of the electronic or electro-optic device200 can be, for example, an n-type or a p-type semiconductor accordingto some embodiments of the current invention. In other embodiments, thesemiconductor layer 208 can be a layer of more than one type ofsemiconductor such as a p-type and an n-type layer, either in verticalor side-by-side arrangement, to provide a device with a p-n junction.

Solution Processed Oxide-Based Semiconductors

Solution processed semiconductors can be used according to someembodiments of the current invention in addition to the sol-gelprocessed dielectric materials. ZnO is an example of semiconductingmaterial that can be used according to some embodiments of the currentinvention. The ZnO semiconducting oxide is a relatively nontoxicn-channel inorganic field effect transistor (FET) semiconductor withhigh electron mobility (1-10 cm2/Vs), excellent environmental stability,and high transparency. (U. Ozgur, Y. I. Alivov, C. Liu, A. Teke, M. A.Reshchikov, S. Dogan, V. Avrutin, S. J. Cho, and H. Morkoc, Acomprehensive review of ZnO materials and devices, Journal of AppliedPhysics 98 (2005). R. L. Hoffman, B. J. Norris, and J. F. Wager,ZnO-based transparent thin-film transistors, Applied Physics Letters 82,733 (2003).) Thin films of ZnO semiconductor can be prepared by severalsolution processes including spin coating, dip coating, hydrothermalprocess, and sol-gel methods. (J. H. Kim, E. M. Kim, D. Andeen, D.Thomson, S. P. DenBaars, and F. F. Lange, Growth of heteroepitaxial ZnOthin films on GaN-Buffered Al2O3(0001) substrates by low-temperaturehydrothermal synthesis at 90 degrees C., Advanced Functional Materials17, 463 (2007); C. S. Li, Y. N. Li, Y. L. Wu, B. S. Ong, and R. O.Loutfy, ZnO field-effect transistors prepared by aqueous solution-growthZnO crystal thin film, Journal of Applied Physics 102 (2007); C. S. Li,Y. N. Li, Y. L. Wu, B. S. Ong, and R. O. Loutfy, Performance improvementfor solution-processed high-mobility ZnO thin-film transistors, Journalof Physics D-Applied Physics 41 (2008); Y. Natsume and H. Sakata, Zincoxide films prepared by sol-gel spin-coating, Thin Solid Films 372, 30(2000); B. J. Norris, J. Anderson, J. F. Wager, and D. A. Keszler,Spin-coated zinc oxide transparent transistors, Journal of PhysicsD-Applied Physics 36, L105 (2003); B. S. Ong, C. S. Li, Y. N. Li, Y. L.Wu, and R. Loutfy, Stable, solution-processed, high-mobility ZnOthin-film transistors, Journal of the American Chemical Society 129,2750 (2007); B. N. Pal, J. Sun, B. J. Jung, E. Choi, A. G. Andreou, andH. E. Katz, Pentacene-zinc oxide vertical diode with compatible grainsand 15-MHz rectification, Advanced Materials 20, 1023 (2008); B. N. Pal,P. Trottman, J. Sun, and H. E. Katz, Solution-deposited zinc oxide andzinc oxide/pentacene bilayer transistors: High mobility n-channel,ambipolar and nonvolatile devices, Advanced Functional Materials 18,1832 (2008).) The ZnO film may be formed through a specific thermaltreatment of a solution-fabricated ZnO precursor film. By controllingZnO film thickness, the FET mobility may be controlled. In an exemplaryembodiment, FET mobility may be higher than amorphous silicon and othersimilar ZnO transistor semiconductors in air.

Mixed oxides based on ZnO can have even higher FET mobilities, >10cm²/Vs, while maintaining transparency. They are deposited from mixedhalide solutions. For example, Zinc tin oxide (ZTO) may be prepared byspincoating a solution of the chlorides from acetonitrile and convertingthe film to oxide by thermal annealing in air. In an embodiment, thefield effect mobility was 16 cm²/Vs, with an on/off ratio of 105. (S.Jeong, Y. Jeong, and J. Moon, Solution-processed zinc tin oxidesemiconductor for thin-film transistors, Journal of Physical Chemistry C112, 11082 (2008); Y. J. Chang, D. H. Lee, G. S. Herman, and C. H.Chang, High-performance, spin-coated zinc tin oxide thin-filmtransistors, Electrochemical and Solid State Letters 10, 14135 (2007).)The mobility was similar to that obtained by sputtering. (M. G.McDowell, R. J. Sanderson, and I. G. Hill, Combinatorial study of zinctin oxide thin-film transistors, Applied Physics Letters 92 (2008).)

In another embodiment, indium zinc oxide (IZO) may be prepared undervery similar conditions to yield comparable results. (C. G. Choi, S. J.Seo, and B. S. Bae, Solution-processed indium-zinc oxide transparentthin-film transistors, Electrochemical and Solid State Letters 11, H7(2008); D. H. Lee, Y. J. Chang, G. S. Herman, and C. H. Chang, A generalroute to printable high-mobility transparent amorphous oxidesemiconductors, Advanced Materials 19, 843 (2007).)

These compounds, as well as more complicated compositions, may also bedeposited by inkjet printing the precursor solution. Indium oxide itselfwas deposited from a solution that included ethanolamine. In anembodiment, the resulting mobility was 44 cm²/Vs and on/off ratio of 106in a transistor. (H. S. Kim, P. D. Byrne, A. Facchetti, and T. J. Marks,High performance solution-processed indium oxide thin-film transistors,Journal of the American Chemical Society 130, 12580 (2008).) Gallium isan additional element that can be included in these semiconductors insome embodiments of the current invention. (J. K. Jeong, H. J. Chung, Y.G. Mo, and H. D. Kim, Comprehensive study on the transport mechanism ofamorphous indium-gallium-zinc oxide transistors, Journal of theElectrochemical Society 155, H873 (2008). W. T. Lim, J. H. Jung, S. H.Kim, D. P. Norton, V. Craciun, S. J. Pearton, F. Ren, and H. Shen, Highperformance indium gallium zinc oxide thin film transistors fabricatedon polyethylene terephthalate substrates, Applied Physics Letters 93(2008).)

Integration of Oxide Semiconductors and Dielectrics for CapacitanceEnhancement and Tuning

There is very limited work on the use of semiconductors as capacitorelectrodes with the deliberate intent to decrease the effectivethickness of the dielectric, and thereby increase the capacitance. Intransistors, the gate capacitance provides the impetus to form aconductive channel in the semiconductor at the interface with thedielectric. Capacitance-voltage plots reveal the presence of thischannel in the form of an altered slope at the threshold voltage, wherethe channel has just formed and the transistor just reaches theaccumulation regime. An example of this phenomenon with oxide materialsused ZnO and Ta₂O₅ as semiconductor and dielectric, respectively (FIG.3). (S. K. Nandi, W. K. Choi, Y. S, Noh, M. S. Oh, S. Maikap, N. M.Hwang, D. Y. Kim, S. Chatterjee, S. K. Samanta, and C. K. Maiti,Investigations on Ta₂O₅/ZnO insulator-semiconductor interfaces,Electronics Letters 38, 1390 (2002).) An unusually dramatic increase incapacitance in the accumulation region was observed, correlated with amaximum in the alternating current conductance.

In some metal-insulator-semiconductor structures, an interface layer waspresent. The interface layer may consist of a mixed phase ofsemiconductor-derived and dielectric-derived atoms, having a higherconductivity or polarizability than the dielectric phase alone, thoughmost likely with low dielectric strength. In an embodiment, a zirconiumsilicate interlayer was formed when ZrO₂ was deposited on Si, loweringthe effective dielectric thickness and raising the specific capacitance.(Y. S. Lin, R. Puthenkovilakam, J. P. Chang, C. Bouldin, I. Levin, N. V.Nguyen, J. Ehrstein, Y. Sun, P. Pianetta, T. Conard, W. Vandervorst, V.Venturo, and S. Selbrede, Interfacial properties of ZrO₂ on silicon,Journal of Applied Physics 93, 5945 (2003).) On the other hand, a lowerdielectric constant mixed material formed between Si and lanthanumaluminum oxide. (V. Edon, M. C. Hugon, B. Agius, C. Cohen, C. Cardinaud,and C. Eypert, Structural and electrical properties of the interfaciallayer in sputter deposited LaAlO3/Si thin films, Thin Solid Films 515,7782 (2007).) In other embodiments, the interface between an oxidedielectric and a semiconductor substrate is sharp. Zhang et aldetermined voltage-dependent capacitance of aluminum/zirconium oxidelayers on Si at MHz frequencies and designated the minority carriers inthe Si as limiting the high frequency capacitance. (N. L. Zhang, Z. T.Song, Q. W. Shen, Y. J. Wu, Q. B. Liu, C. L. Lin, X. Z. Duo, L. R. Meng,Y. F. Ding, and Z. Q. Zhu, High frequency capacitance-voltagecharacterization of Al2O3/ZrO2/Al2O3 in fully depletedsilicon-on-insulator metal-oxide-semiconductor capacitors, AppliedPhysics Letters 83, 5238 (2003).) Another group examined capacitance ofa mixed La Al oxide dielectric on InGaAs at frequencies up to 1 MHz,with changes in the capacitance-frequency relationship in the inversionregion indicating minority carrier participation. (N. Goel, P. Majhi, W.Tsai, M. Warusawithana, D. G. Schlom, M. B. Santos, J. S. Harris, and Y.Nishi, High-indium-content InGaAs metal-oxide-semiconductor capacitorwith amorphous LaAlO₃ gate dielectric, Applied Physics Letters 91(2007).) An equivalent dielectric thickness of about 1 nm was shown forGa/Gd oxide with alumina protection on the same semiconductor. (K. H.Shiu, T. H. Chiang, P. Chang, L. T. Tung, M. Hong, J. Kwo, and W. Tsai,1 nm equivalent oxide thickness in Ga2O3(Gd2O3)/In0.2Ga0.8Asmetal-oxide-semiconductor capacitors, Applied Physics Letters 92(2008).)

Some embodiments of the current invention can include the concept offorming a mixed interfacial phase between a semiconductor layer and anionically polarizable solid for enhancing or controlling capacitance.

Some Applications

The use of ionically polarized organic solids as dielectrics can impacta wide range of applications related to electronics and energygeneration. For example, an alternative for flexible electrical storagecapacitors may be introduced. Pillared alumina capacitors mounted onflexible metal foils can be capable of high electrical energy storagedensity at elevated temperatures, especially in rolled form, accordingto some embodiments of the current invention. Mobility-capacitanceproducts of flexible field-effect transistors can lower the voltages atwhich useful output currents can be obtained while maintaining fastswitching ability (mostly dependent on mobility and source-drainseparation) according to some embodiments of the current invention.Furthermore, transparent materials may facilitate the manufacture ofdevices such as display backplanes in some embodiments. Semiconductiveoxides may also be useful as optical spacers in organic solar cells, inwhich thickening of the electron-injecting electrodes with transparentoxides defines incident light wave maxima so that the highest lightintensity is coincident with the light-absorbing layers. (J. Y. Kim, S.H. Kim, H. H. Lee, K. Lee, W. L. Ma, X. Gong, and A. J. Heeger, Newarchitecture for high-efficiency polymer photovoltaic cells usingsolution-based titanium oxide as an optical spacer, Advanced Materials18, 572 (2006); J. K. Lee, N. E. Coates, S. Cho, N. S. Cho, D. Moses, G.C. Bazan, K. Lee, and A. J. Heeger, Efficacy of TiOx optical spacer inbulk-heterojunction solar cells processed with 1,8-octanedithiol,Applied Physics Letters 92 (2008).) Mixed ZnO-based semiconductors withbroader distributions of carrier energies may show increased thermopowercompared to homogeneous materials, as electrons will be injected intoenergy levels associated with impurity atoms, where there are fewerstates, and will then be transported within a matrix of majority Znatoms.

The voltage dependence of the capacitance may be used as a circuittuning element, for example, to change RC time constants and/or resonantfrequencies by applying external voltages to circuits for signalprocessing. Such tuning is already possible with capacitors that vary inposition relative to the rest of the circuit, or have differing fixedcapacitance values. (E. Brennan, V. E. Fusco, and A. G. Schuchinsky,Signal frequency identification using anisotropic propagationcharacteristics of capacitively tuned L-C grids, Electronics Letters 42,981 (2006); W. Chaivipas, K. Okada, and A. Matsuzawa, Spatialsensitivity of capacitors in distributed resonators and its applicationto fine and wide frequency tuning digital controlled oscillators, IeiceTransactions on Electronics E91C, 918 (2008); J. M. Drozd and W. T.Joines, A capacitively loaded half-wavelength tapped-stub resonator,Ieee Transactions on Microwave Theory and Techniques 45, 1100 (1997); K.Y. Lee, S. Mohammadi, P. K. Bhattacharya, and L. P. B. Katehi, Compactmodels based on transmission-line concept for integrated capacitors andinductors, Ieee Transactions on Microwave Theory and Techniques 54, 4141(2006).) Consequently, some applications of the current invention canprovide improvements over such circuits.

Example 1

According to an embodiment of the current invention, an SBA film may becreated using the following procedure. SBA glass may be synthesized byfollowing the widely cited sol-gel procedure of Yoldas (B. E. Yoldas,Alumina Gels that form Porous Transparent Al₂O₃, Journal of MaterialsScience 10, 1856 (1975); B. E. Yoldas, Transparent Porous Alumina,American Ceramic Society Bulletin 54, 286 (1975); B. E. Yoldas, AluminaSol Preparation from Alkoxides, American Ceramic Society Bulletin 54,289 (1975)), but with an additional Na₂O precursor. The target gelcomposition was 1Na₂O to 11 Al₂O₃. This was chosen so that it canexactly match the formula of SBA crystal. The starting materials werealuminium secondary butoxide [(Al(OC₄H₉)₃] and sodium acetate. Ameasured amount (0.041 mg) of sodium acetate was dissolved in 50 mlwater. The solution was heated to 90° C. Aluminium secondary butoxide isa viscous and moisture-reactive liquid, but when it is heated at 90° C.,both the viscosity and reactivity are highly reduced. Hence, 1.41 ml[(Al(OC₄H₉)₃] was heated at 90° C. with vigorous stirring. The sodiumacetate solution at 90° C. was added to it under continuous stirring.The temperature of this mixture was then increased to 95° C. and keptstirring for half an hour to form an AlO(OH) precipitate. The hydrolysistemperature was the highest temperature that would not lead to violentboiling caused by the exothermic hydrolysis and condensation reactions.In the next step, a dilute mixed acid (0.2N HNO₃ and 0.2N HCl, 1:1ratio) was used in the peptization procedure. In this process acids areadded very slowly and ultimately the sol becomes transparent. The solwas kept under continuous stirring at 95° C. for half an hour. Withsufficient water removal, the sol become a clear solution and approachedthe gel point. The clear gel was then filtered through a syringe filter.The filtrate gel was coated over indium tin oxide (ITO)-coated quartzwafers and highly doped silicon wafers. The ITO-coated quartz substrateswere dip-coated in the gel solution and dried at 100° C. for one hour.As a result, a continuous layer of glass is formed on the ITO. Thisgel-derived glass layer was then subjected to high temperature heattreatment for crystallization, in a 750° C. furnace. During a fewminutes of treatment, nucleation sites for SBA crystallization areformed. Then the temperature was increased to 850° C. and kept for fewminutes more for complete crystallization of SBA. The dip coating andannealing process was then repeated once more, giving a continuous layerof SBA crystal. Similar gel-to-crystallite conversation processes havesbeen reported by a number of groups. (V. Jayaraman, G. Periaswami, andT. R. N. Kutty, Preparation of potassium beta aluminas bygel-to-crystallite conversion and their characterisation, Journal ofMaterials Chemistry 8, 1087 (1998); V. Jayaraman, G. Periaswami, and T.R. N. Kutty, Influence of the preparative conditions on the precursorphases formed during the synthesis of beta-alumina by the wet chemicalgel to crystallite conversions, Materials Chemistry and Physics 52, 46(1998).) A powder that we produced by the same process (except for thecoating step) gave an x-ray diffraction pattern (FIG. 4) that wasindexed to the beta phase. (R. Subasri, T. Mathews, O. M. Sreedharan,and V. S. Raghunathan, Microwave processing of sodium beta alumina,Solid State Ionics 158, 199 (2003).)

SBA was also deposited on n-doped Si wafers, which were first cleaned inpirhana solution to make the surface hydrophilic. Wafers were then spincoated (3000 rpm/30 sec) with gel solution and dried and annealed (onetime) as for the ITO substrates. After SBA coating, both types ofsubstrates were then spin coaled with dilute (2 times diluted for ITOsubstrate, and 5 times diluted for Si⁻⁻ substrate) sol and annealed at150° C. As a result, a thin layer of glassy oxide covered and smoothedthe surface. The resulting dielectric layer was suitable for use as aFET gate insulator, as established by atomic force microscopy.

FIG. 5 shows Capacitance-Frequency (C-f) measurements of the SAB filmcarried out on an ITO/SBA/Au structure with a HP 4192A LF impedanceanalyzer over the frequency range from 50 Hz to 1 MHz. A 75 nm thicklayer of SBA film was grown on an ITO coated quartz substrate and Au wasused as top electrode. The capacitance of this dielectric layer at 50 Hzis 2.5 μF/cm², which is much greater than that of typical inorganicfilms. For comparison, a 75 nm thick layer of SiO₂ has a capacitance of38 nF/cm². The calculated dielectric constant of this SAB film is 211.This value is much higher than alumina dielectric (9.2) and otherinorganic high-dielectric materials used in FETs such as HfO₂ (25) andZrO₂ (25). (J. Robertson, High dielectric constant oxides, EuropeanPhysical Journal-Applied Physics 28, 265 (2004).) The SBA filmcapacitance decreases with frequency as expected, because the ionmobilities limit the polarization response time. However, thecapacitance is 350 nF/cm² at 1 MHz. This implies that high-frequency/lowvoltage switching of FETs and the RC time constants of circuits shouldbe possible. The film was quite continuous, as shown by thecross-sectional scanning electron micrograph of a film prepared inparallel on a silicon wafer, as illustrated in FIG. 6.

Capacitance in many conventional dielectrics is dominated by chargearriving at and accumulating over the film surfaces, but in the case ofsol-gel-derived SBA, the magnitude of the polarization from displacementof Na⁺ ions may be much larger, leading to much higher capacitance. Thefreedom of movement of the cations and the short displacement distancesperpendicular to the MO layers ensure that significant capacitance isexhibited even at high frequencies.

The high capacitance of SBA may be utilized to lower the operating gatevoltage of solution-processed and organic semiconductor-basedfield-effect transistors (FETs) on Si wafers. FETs that would haverequired tens of volts to switch on completely may be switched on withsingle volts. For example, we used ZnO thermally converted from solublezinc acetate as a semiconductor in the FET embodiment depicted in FIG.7. The mobility of the ZnO was in the range of 0.1-1 cm2/Vs and thecapacitance of the dielectric was 400 nF/cm². This is one of the highermobility-capacitance products reported for FETs with solution-depositedactive materials. The dielectric strength of the SBA was >1 MV/cm,consistent with low vertical conductivity and low leakage of ions out ofthe dielectric film into the semiconductor or the contacts.

An even higher capacitance-mobility product may be obtained from anexemplary transistor comprising a solution-processed transparent zinctin oxide (ZTO) semiconductor deposited over SBA-coated ITO-quartzsubstrates. The exemplary transistor may be formed in the followingmanner. A metal halide precursor solution was prepared by dissolving0.05 M of ZnCl₂ and 0.05 M SnCl₂ in 25 mL acetonitrile solvent (S.Jeong, Y. Jeong, and J. Moon, Solution-processed zinc tin oxidesemiconductor for thin-film transistors, Journal of Physical Chemistry C112, 11082 (2008); Y. J. Chang, D. H. Lee, G. S. Herman, and C. H.Chang, High-performance, spin-coated zinc tin oxide thin-filmtransistors, Electrochemical and Solid State Letters 10, H135 (2007))and mixing by ultrasonicating. SBA dielectric-coated substrate was firstkept in NaOH (1M) solution for 10 min to make it hydrophilic, thenwashed in water and dried in dry nitrogen. The substrate was thendip-coated with this solution at a speed approximately 2 mm/sec with anangle 60° to the horizontal and immediately placed on a 70° C. hotplate. (B. N. Pal, J. Sun, B. J. Jung, E. Choi, A. G. Andreou, and H. E.Katz, Pentacene-zinc oxide vertical diode with compatible grains and15-MHz rectification, Advanced Materials 20, 1023 (2008).) This processwas repeated four times. The coated substrate was inserted into apreheated 600° C. furnace and kept for 15 minutes to form a thin layerof continuous polycrystalline ZTO nanoparticle film. The resultant ZTOfilm thickness is around 60 nm, confirmed by SEM images. Subsequently,100 nm-thick aluminum electrodes were deposited using a slim bar TEMgrid (200 mesh) as shadow mask. Output characteristics of the device areshown in FIG. 8.

Specifically, FIG. 8 shows open atmosphere I_(D)-V_(D) characteristicsof a ZTO FET with W/L ratio of 10 (120 μm/12 μm). The applied drainvoltage (V_(D)) is swept from 0 to 2 V in both forward and reversedirections and gate voltage (V_(G)) is stepped between −0.3 and +1.5 V.This figure shows the clear linear and saturation regions of the outputcharacteristics with very negligible hysteresis. The dielectricbreakdown voltage is about 15 V, so there is some latitude to increasevoltages further. The ON/OFF ratio of the device is 19³. The saturatedmobility for this device is 24.1 cm²/V-s. For a series of twenty similardevices, the mobility is in the range of 18-29 cm²/Vs, calculatedassuming a “1 Hz-frequency” extrapolated capacitance of 3 μF/cm², andwith On/Off ratio remaining at 10³. The mobility times capacitance/areaproduct of 70 μF/Vs (μS/V) is extremely high for a nonsilicon,nonsputtered FET (H. Klauk, U. Zschieschang, and M. Halik, Low-voltageorganic thin-film transistors with large transconductance, Journal ofApplied Physics 102 (2007)).

The capacitance of an oxide dielectric-semiconductor bilayer is indeedvoltage-dependent. FIG. 9 shows the capacitance as a function of appliedDC voltage for a capacitor with the structure ITO-SBA-Au. Of course, ITOis quite conductive and does not really function as a semiconductor.Even so, at four different frequencies between 10 and 100 kHz, thecapacitance changes by 10% over an applied voltage range of 7 V. Thereis little sign of a threshold or turn-on voltage. FIG. 10 shows a C-Vplot for a device with ZTO interposed between the dielectric and onecontact. There is a clear increase in capacitance at the voltage where atransistor made from the same materials would turn on. The increase isby about a factor of five, indicating significant circuit tuningability. Use of a thinner dielectric may make the increase even larger.

Example 2

According to an embodiment of the current invention, an SBA film was becreated using the following procedure. SBA glass, may be synthesized byfollowing the widely cited sol-gel procedure of Yoldas (B. E. Yoldas,Alumina Gels that form Porous Transparent AL2O3, Journal of MaterialsScience 10, 1856 (1975); B. E. Yoldas, Transparent Porous Alumina,American Ceramic Society Bulletin 54, 286 (1975); B. E. Yoldas, AluminaSol Preparation from Alkoxides, American Ceramic Society Bulletin 54,289 (1975).) The target gel composition was 1Na₂O, 11 Al₂O₃. This waschosen such a way, so that it could exactly mach with formula of SBAcrystal. The starting materials were Aluminium Secondary Butoxide[(Al(OC₄H₉)₃] and Sodium Acetate. A measure amount (0.041 mg) of sodiumacetate was dissolved in 25 ml water. The solution was heated to 90° C.Aluminium Secondary Butoxide is a viscous and reactive with atmosphericmoisture at room temperature. But when it is heated at 90° C., both theviscosity and reactivity are highly reduced. For this reason 1.41 ml[(Al(OC₄H₉)₃] was heated at 90° C. with vigorous stirring. Then Sodiumacetate solution of 90° C. was added with it under continuous stirring.Temperature of this mixture was then increased to 95° C. and kept forhalf an hour under stirring condition for hydrolysis and condensation ofaluminium alkoxide to form an AlO(OH) precipitate. The hydrolysistemperature was chosen because of it is the highest temperaturecompatible with avoiding violent boiling caused by the exothermichydrolysis and condensation reactions. In the next step, acids (2N HNO₃and 2N HCl, 1:1 ratio) were used in the peptization procedure. In thisprocess acids are added very slowly and ultimately sol becomestransparent. The sol was kept under continuous stirring at 95° C. forhalf an hour. With sufficient water removal, the sol become a clearsolution and approaches the gel point. The clear gel was then filteredby using syringe filter. Then this filtrate gel was spin coated over ahighly dope silicon wafer. Then it was dried at 100° C. for one hour. Asa result a contentious layer of glass is formed on the Si wafer. Thisgel derived glass layer was then subjected to high temperature heattreatment for crystallization. For this it was inserted in a hightemperature furnace and it temperature was set to 750° C. and kept forfew minutes. During this heat treatment number of nucleation site forSBA crystal is formed. Then temperature was increased to 830° C. andkept for few minutes more for complete crystallization of SBA. In thisperiod glass layer is totally converted to a continuous layer of SBAcrystal. Now this layer can behave as gate insulator of FET. Then asolution processed zinc oxide FET has been fabricated using SBA coatedwafer. For solution processed ZnO films, we used zinc acetate [Zn(OAc)₂](40 mM) and 2-ethanolamine (5 mM) solutions in ethanol as a solvent. Thesubstrate was dip-coated by this solution with a speed approximately 2mm/sec with an angle 60° to the horizontal and immediately placed on a70° C. hot plate. This process was repeated two times. The coatedsubstrate was inserted into a preheated 500° C. furnace and kept for 15minutes to form a thin layer of continuous polycrystalline ZnOnanoparticle film. By using this kind of heat treatment, unidirectionalZnO nanoparticle films can be formed where the c-axis of the ZnO hcpcrystal is perpendicular to the substrate. This oriented ZnO film givesa very high field effect mobility. Subsequently, 50 nm-thick aluminumelectrodes were deposited using a parallel TEM grid (200 mesh) as shadowmask. Transistor characteristics were obtained using a semiconductorparameter analyzer (Agilent 4155C). All electrical characterizationresults reported in this specification were done in ambient atmosphericconditions.

FIG. 11 shows open atmosphere I_(D)-V_(D) characteristics of ZnOtransistors. The applied drain voltage (V_(D)) is I V and gate voltage(V_(G)) sweep between −1 V to 1 V. This figure shows the linear andsaturation region of the output characteristics, although the transistoroperates in depletion mode with an appreciable drain current at zerogate voltage (V_(G)) and exhibits excellent drain current saturation.Such non-ideal effects are commonly observed in oxide FETs. FIGS. 12 and13 illustrate the same characteristics of an identical device fordifferent V_(G) but with V_(D)=2V. From these figures it is very clearthat the drain current increase with V_(G) but 2V drain voltage issufficient to show clear linear and saturation region of the outputcharacteristics. FIG. 14 shows I_(D)-V_(D) characteristics with highergate voltage (V_(G)) and drain voltage (V_(D)). Since the gate insulatoris not an ultra thin layer, it may work nicely in higher voltage aswell.

FIG. 15 shows I_(D)-V_(G) measurements (transfer characteristic) of theZnO FET with a 20 volt source-to-drain voltage in an ambient atmosphere.The gate-to-source voltage (V_(G)) was swept between −2V to +2V. FIG. 16shows the same transfer characteristics with semi-log scale. It showsthat the ON/OFF ratio of the device is 10×10².

Additional Examples of Tonically Polarizable Oxide Dielectrics

One can vary ions in β-alumina analogues to observe the effect onfrequency-dependent dielectric constant, dissipation factor, anddielectric strength, which determine energy density and rate andefficiency of energy release in capacitors, for example. β-aluminadielectrics can be formed with a range of included monovalent, divalent,and trivalent ions, by incorporation into sol-gel precursors or by ionexchange. Versions of β-alumina with a wide variety of intercalatedcations are known, including lithium, potassium, calcium, silver,strontium, and lanthanum. (R. Chung and S. W. de Leeuw, Influence ofdipolar interactions on the conduction mechanism of Li⁺-beta-alumina:Molecular Dynamics study, Solid State Ionics 176, 599 (2005); T. Goto,G. He, T. Narushima, and Y. Iguchi, Application of Sr beta-alumina solidelectrolyte to a CO2 gas sensor, Solid State Ionics 156, 329 (2003); Y.R. Hong, C. J. Jin, and J. L. Sun, in High-Performance Ceramics 2001,Proceedings, edited by J. P. W. Gong, 2002), Vol. 224-2, p. 183. V.Jayaraman, G. Periaswami, and T. R. N. Kutty, Preparation of lithiumB″-alumina by the ion-exchange reaction, Materials Research Bulletin 33,1811 (1998); O. Kamishima, Y. Iwai, J. Kawamura, and T. Hattori, Defectmodes around low-lying phonon in Ag beta-alumina by Raman scatteringwith high resolution, Solid State Ionics 179, 780 (2008); A. Y. Zhang,T. Akashi, B. P. Zhang, T. Goto, and T. Zhang, Electrical conductivityand ionic transport number of Sr beta-alumina single crystals preparedby a floating zone method, Solid State Ionics 176, 2319 (2005); K. Shqauand H. Nate, Thermodynamic stability of potassium-beta-alumina, Journalof the American Ceramic Society 88, 2894 (2005); K. Funke and R. D.Banhatti, (2007), p. 1942.) The cations may be present as mixtures, andat varied concentrations. The layered solids can also be examined fortheir applicability as dielectrics in capacitors or transistors, forexample.

The various cations can be incorporated in two ways. The first is tosubstitute the appropriate oxides for sodium oxide in the sol-gel-basedfilm preparation described above. The second is to simply immersecrystallized films of SBA molten salts (for example, halides andnitrates) containing the desired alternative cations. The rapiddiffusion and exchange of cations in SBA under these conditions has beendemonstrated for a wide variety of cations, including those mentioned inthe preceding paragraph. (S. Sattar, B. Ghosal, M. L. Underwood, H.Mertwoy, M. A. Saltzberg, W. S. Frydrych, G. S. Rohrer, and G. C.Farrington, Synthesis of divalent and trivalent BETA″-ALUMINAS byIon-exchange, Journal of Solid State Chemistry 65, 231 (1986); G. W.Schafer and W. Weppner; Preparation of Divalent Beta-alumina Ceramicsvia Ion-exchange from K-ALUMINA AND NA-BETA″-ALUMINA Cermaics, SolidState Ionics 53-6, 559 (1992); F. Tietz and W. Urland, LanthanideIon-exchange in Sodium,-BETA-ALUMINA, Solid State Tonics 46, 331(1991).) To produce larger changes in the dielectric properties,mechanical flexibility, and possibly surface energies and topographies,SBA may be exchanged with organic ions as well.

Layered alumina or other dielectrics that can be prepared attemperatures below those at which “high-temperature” polymers break downcan be used for flexible transistors and transistor-based circuits onpolymer substrates. However, if annealing temperatures of 700-900° C.are required, then metal foils can be used as substrates for flexibletransistor circuits employing the described materials. While processingmight not by quite as convenient as for plastic substrates, the eventualcomponents can be usable at significantly elevated temperatures. Aprocess methodology for the use of steel foils for flexible transistorsis well developed. (A. Z. Kattamis, N. Giebink, I. C. Cheng, S. Wagner,S. R. Forrest, Y. Hong, and V. Cannella, Active-matrix organiclight-emitting displays employing two thin-film-transistor a-Si: Hpixels on flexible stainless-steel foil, Journal of the Society forInformation Display 15, 433 (2007); M. Wu, X. Z. Bo, J. C. Sturm, and S.Wagner, Complementary metal-oxide-semiconductor thin-film transistorcircuits from a high-temperature polycrystalline silicon process onsteel foil substrates, Ieee Transactions on Electron Devices 49, 1993(2002); M. Wu, K. Pangal, J. C. Sturm, and S. Wagner, High electronmobility polycrystalline silicon thin-film transistors on steel, foilsubstrates, Applied Physics Letters 75, 2244 (1999).) These transistorsuse silicon-based transistors and dielectrics, but the steel platformcan be adapted for use with the oxide materials according to someembodiments of the current invention.

This specification described various embodiments of the invention insome detail. For example, combinations of sol-gel processed gatedielectrics and electron-carrying semiconductors can be used infabricating field-effect transistors that operate in the voltage rangeof 0.1-10 volts according to some embodiments of the current invention.The dielectrics can be bulk network solids or monolayers, for example.The semiconductors can be inorganic oxides or condensed ring organiccompounds in some embodiments. The transistors can be useful forcircuits on large-area, irregular, and/or low-melting substrates in someembodiments. Applications can include display backplanes, sensor arrays,flexible amplifiers, and low level memory tags, for example. Thesedevices can also be useful for educational demonstrations and used ineducational kits.

Organic and printed circuits are generally tested and operated atvoltages in the range of 10-100 V. This is much too high for manyapplications where power is limited, such as with small batteries orradiofrequency power sources. The high voltages are correlated withthick gate dielectrics that demand high voltages in order to form thecharge transport channel at the gate dielectric-semiconductor interfacein a field-effect transistor. Thinner gate dielectrics and dielectricswith higher dielectric constant have higher capacitance and thereforerequire lower voltages to induce the same charge density into thechannel. A major challenge for printed electronics is to process gatedielectrics without capital-intensive, slow processes generallyassociated with silicon technology. High-capacitance gate dielectricsmade by printing methods generally suffer from high leakage currentsthat override the switching action of the transistor. Some embodimentsof the current invention can overcome these problems.

In describing embodiments of the invention, specific terminology isemployed for the sake of clarity. However, the invention is not intendedto be limited to the specific terminology so selected. Theabove-described embodiments of the invention may be modified or varied,without departing from the invention, as appreciated by those skilled inthe art in light of the above teachings. It is therefore to beunderstood that, within the scope of the claims and their equivalents,the invention may be practiced otherwise than as specifically described.

1. An electronic or electro-optic device, comprising: a first electrode;a second electrode spaced apart from said first electrode; and adielectric layer disposed between said first and second electrodes,wherein said dielectric layer comprises electrically insulating planarlayers with intercalated ions therebetween, said electrically insulatingplanar layers providing a barrier to impede movement of saidintercalated ions to said first and second electrodes under an appliedvoltage while permitting a polarization of said dielectric layer whilein operation.
 2. An electronic or electro-optic device according toclaim 1, wherein said electrically insulating planar layers aremetal-oxide planar layers.
 3. An electronic or electro-optic deviceaccording to claim 2, wherein said metal-oxide planar layers comprisealuminum oxide.
 4. An electronic or electro-optic device according toclaim 1, wherein said intercalated ions are sodium ions.
 5. Anelectronic or electro-optic device according to claim 1, wherein saidintercalated ions are selected from at least one of sodium, potassium,calcium, silver, strontium and lanthanum ions.
 6. An electronic orelectro-optic device according to claim 1, wherein said dielectric layercomprises at least one of sodium beta alumina or sodiumbeta-double-prime alumina.
 7. An electronic or electro-optic deviceaccording to claim 1, wherein said electronic or electro-optic device isa capacitor.
 8. An electronic or electro-optic device according to claim1, further comprising a semiconductor layer disposed between said firstelectrode and said second electrode.
 9. An electronic or electro-opticdevice according to claim 8, further comprising a third electrode spacedapart from said first and second electrodes such that said dielectriclayer and said semiconductor layer are arranged between said thirdelectrode and said second electrode.
 10. An electronic or electro-opticdevice according to claim 9, wherein said electronic or electro-opticdevice is a field effect transistor.
 11. An electronic or electro-opticdevice according to claim 9, wherein said first and third electrodes arein contact with said semiconductor layer to provide drain and sourceelectrodes, respectively, and said second electrode provides a gateelectrode such that said electronic or electro-optic device is a fieldeffect transistor.
 12. An electronic or electro-optic device accordingto claim 9, wherein said semiconductor layer is an n-type semiconductorlayer.
 13. An electronic or electro-optic device according to claim 12,wherein said n-type semiconductor layer is an inorganic n-typesemiconductor layer.
 14. An electronic or electro-optic device accordingto claim 12, wherein said n-type semiconductor layer is an organicn-type semiconductor layer.
 15. An electronic or electro-optic deviceaccording to claim 1, further comprising a hybridsemiconductor-dielectric layer disposed between said first electrode andsaid second electrode.
 16. An electronic or electro-optic deviceaccording to claim 12, further comprising a p-type semiconductor layerdisposed between said first and second electrodes in contact with saidn-type semiconductor layer to provide an electronic or electro-opticdevice having a p-n junction.
 17. An electronic or electro-optic deviceaccording to claim 16, wherein said p-type semiconductor layer is anorganic semiconductor layer.
 18. An electronic or electro-optic deviceaccording to claim 16, wherein said n-type and p-type semiconductorlayers are arranged laterally in a side-by-side configuration.
 19. Anelectronic or electro-optic device according to claim 16, wherein saidn-type and p-type semiconductor layers are arranged with one layerdisposed on top of the other.
 20. A method of producing an electronic orelectro-optic device, comprising: providing a first electrode; providingsecond electrode spaced apart from said first electrode; and disposing adielectric layer between said first and second electrodes, wherein saiddielectric layer comprises electrically insulating planar layers withintercalated ions therebetween, said electrically insulating planarlayers providing a barrier to impede movement of said intercalated ionsto said first and second electrodes under an applied voltage whilepermitting a polarization of said dielectric layer while in operation.